If I had a handy-dandy Custom Planet Extruder™, and could pop out planets of whatever size and composition I wanted, I’d like to start over with a new solar system that has more useful real estate than we do.
How should I set this new system up? (No Ringworlds, Dyson spheres, or the like need apply – I’m just talking a star of any variety that would work best, plus a bunch of habitable planets in stable orbits. How many can I have?)
Just start making them and giving them a shove. Some will find a stable orbit. If two smash into each other, hey, free moon!
Stephen Dole’s Habitable Planets for Man used to be the standard ref of this:
Since then, there have been others:
There have GOT to be internet sites and discussions on this.
Like this:
http://home.comcast.net/~brons/NerdCorner/StarGen/StarGen.html
You can download HPfM, apparently:
http://futurismic.com/2007/07/18/worldbuilders-bible-available-for-download/
Klemperer Rosettes are the way to go. Run four moderately large (about 10-20 Earth masses) planets at 12:00, 3:00, 6:00, & 9:00. These can have habitable moons & companions (maybe even Earth-type planets in their outer equilibrium points). To keep the Rosette stable, run class M planets at 1:30, 4:30, 7:30, & 10:30.
There are two ways to get more real estate in a star system: use bigger planets or increase the size of the star’s habitable zone. The habitable zone gets wider the farther out it is — if you do the thermodynamic calculations, you find that the “width” of the habitable zone is about 10-20% of its distance from the sun. I doubt that this range will be wide enough to establish a stable orbital resonance, though, so you may be out of luck in shoehorning extra planets into the habitable zone.
Your best bet would be to have increasing amounts of greenhouse gases in the atmosphere of the outer planets. I don’t know if there’s an upper limit on this (if nothing else, you want to keep enough oxygen in the atmosphere, and make sure it doesn’t become too thick to breathe), but in principle the more massive you make a planet, the thicker its atmosphere will be and the warmer it will be at the surface. Carbon dioxide, methane, and (to a certain extent) water vapor will give you more greenhouse-warming bang for your buck. (Ozone would too, but it’s not stable, and the further out you go from your star, the more trouble you’re going to have producing it in the upper atmosphere.)
Modify that. Six, not four, take advantage of the Lagrange points of their immediate neighbors, producing additional stability.
Make it six Jovians with multiple Earthlike satellites in Earth orbit (or the equivalent for the luminosity of the relevant star), then six super-Jovians in roughly Mars orbit (same caveat), also with multiple Earthlike satellites, and at a surface temperature where their infrared radiation heats the planets to Terrestrial levels.
The trouble for stars that are brighter than the sun is that they are brighter because they are more massive, which means gravity is higher which means more nuclear fusion. More nuclear fusion means faster nuclear fusion. So massive hot stars burn out very quickly and you don’t have much time for life to evolve, plus they put out a lot more higher-energy EM radiation which could be bad for children and other living things.
What would be issues with running orbits out of the ecliptic?
Scary conjunctions.
When planets pass each other in different orbital planes, the gravitational attraction between them tends to pull both planets out of their respective orbital planes. That’s not conducive to having a stable orbit.
Klemperer rosettes are only marginally stable; a slight perturbation will cause them to become unstable rather quickly, and once perturbed they tend to fling off wildly in seemingly random directions; this can be demonstrated with a very simple simulation in Matlab or Mathematica (or in Python or C if you don’t mind writing real code), where even tiny rounding errors in the precision of calculations will quickly cause a non-correcting orbit to spin out. Klemperer’s paper actually described a system of equal numbers of two or more different mass bodies orbiting a common barycenter; the type of rosette described by Larry Niven as the Fleet of Worlds is actually a trivial subset which is stable (although again, only marginally so) by inspection.
Of course, with a central massive body such that M >>> m1, m2, m3,… you could put a number of bodies in the same orbit at 60° intervals such that each fell within the other’s libration points. Such a system may be at least marginally stable, especially if M1>>>M2~M3~…, although over time influences between minor bodies would affect each other’s orbits. You could also place one body in orbit of a second in orbit of a third, such that M3<<M2<<M1, provided that the ratios between them are M1/M2 is very large and M2/M3>25; this is, in fact, exactly what we have with the Sol-Earth-Luna system. Getting the density sufficient to hold onto an atmosphere might be pretty tricky, though. You could also put two worlds in a tidally-locked couplet in orbit of a much larger mass with pretty good long term stability as long as they’re reasonably close together.
As for the number and arrangement of stable planar orbits, we’re not sure, although there are suspicious similarities in the spacing of orbits which have caused many to look for resonances in orbits. We don’t have anything definitive for planets, although there are some pretty clear resonances in the Jovian moons. I wouldn’t plan on spacing too many orbits close together in a habitable zone; planetary collisions are a bad day all around.
Very tricky; when dealing with out of plane orbits you have to account for orbital behavior in three dimensions; this is generally contrary to long term stability of the orbit, especially if you have one or more large secondary influences (a Jovian or larger planet).
The real solution for maximizing habitable volume is to get away from planets completely. Spherical worlds are remarkably inefficient–remember, they give minimum surface area for volume–and have all manner of difficulty in getting things like seasons and the length of day just right. Rotating toroids or hollow spheres in massive conjunctive orbits seem like a better use of materials. The o.p. is wise to stay away from Ringworlds and Dyson shells, on the other hand; difficult to stabilize and impossible to defend.
Personally, I’d hide away in the ergosphere of a massive rotating black hole with a good book. Making custom worlds seems like an appealing business until you realize that your customers are going to ask for all sorts of obscene and offensively tacky things. I mean, it’s one thing to go a nice bit of fyords, but when they want a planet that is pink and squishy and squeals every time you walk across it, I’d draw the line.
Stranger
Would hollow spheres save enough material to be worth the ‘useless’ volume in the center, or the larger tracts of difficult to use surface at higher lattitudes? FTM, wouldn’t it be more efficient use of mass to make large, but unenclosed, toroids, and count on the spin to act to keep the atmosphere within the walls? (Sort of a mini-Ringworld, but not centered around the star, and much, much smaller.)
But pink is in this millennium…
That would be an Orbital or similar, then? Yet another reason to love Ian M Banks…
Six super-Jovians at Mars-distance-equivalent orbit? OK, maybe a system the size of–I dunno–Vega’s could get the mass (ours sure doesn’t have it) but aren’t you worried about destabilizing the Jovians at Terra-distance-equivalent?
No spheres? Well, you could always go with a cube shape, give the cartographers fits.
Cubes would be way easier to represent in a 2D map than a sphere.
I’ve noticed the posters in here talking about Jupiter-sized planets, but wouldn’t their gravity crush us? Or are you planning on populating the moons, which would be more earth-sized, with a more earth-like gravity?
S^G
Are those within the theoretical limits of carbon nanotubules, or are we talking pure Unobtanium here? If my math is correct, a 1G gravity and a rate of one revolution per 24 hours gives a diameter of approximately 3,700,000 kilometers!
You want a star system like in Firefly, don’t you?